This invention pertains to apparatus and methods which communicate through frequency hopping spread spectrum (FHSS) networks and, more particularly, to an apparatus having wired or wireless communication capabilities over a frequency hopping spread spectrum network. The apparatus and methods perform a hop sequence alteration based on a neighboring frequency hopping spread spectrum network's hop sequence.
Bluetooth® 1 technology defines a specific wireless frequency hopping spread spectrum communication link operating in the unlicensed ISM band at 2.4 GHz using a frequency hopping tranceiver. It allows real-time voice and data communications between Bluetooth® devices. The communication range of Bluetooth® devices is between 10 and 100 meters, but more commonly is limited to between 10 and 20 meters due to channel noise and power limitations of typical devices. At the present time, the communication bandwidth of Bluetooth® devices is limited to 1 Mbps.
A “physical channel” or “channel” is defined in the Bluetooth® specification as a synchronized sequence of randomized hops between various of 79 or 23 RF channels. Each RF channel occupies 1 Mhz of bandwidth in the 2400-2483.5 MHz RF range. Whether the channel comprises 79 or 23 RF channels is predetermined and depends on the country in which the devices operate.
Bluetooth® devices within communicating range can set up ad-hoc networks by sharing a common physical channel and thereby forming what is known as a “piconet.” A piconet consists of one and only one master device which controls the piconet and a maximum of 7 slave devices. Typically, the master communicates to the slave in a 625 μs time-slot and the slave replies to the master in the very next time-slot. This technique is known as Time Division Duplexing (TDD). The two consecutive slots are referred to as a frame. Each frame can be thought of as a call and response between the master device and the corresponding slave device.
Piconets are formed in an ad hoc fashion by having all devices continuously scan for inquiries in the area where they are operating. Any device, at any time, can initiate an inquiry. The device that initiates the inquiry takes on the role of the master device in the piconet. Devices in the range of the master's inquiry reply to the inquiry. These replying devices assume the role of a slave device in the piconet. All devices can have the capacity to fulfill both the master role and the slave role. The distinction between master and slave allows easier synchronization over the frequency hopping spread spectrum communications link. All slaves synchronize to the master and the master sets the frequency hopping sequence.
A Bluetooth® device can participate in more than one piconet by applying time multiplexing. To participate on a selected one of several channels/piconets, the device uses the associated master device address and the master clock value of the selected channel, and locally applies a proper time shift to obtain the correct phasing therefore.
A Bluetooth® unit can act as a slave in several piconets, but only as a master in a single piconet. Thus, what might be considered as two separate piconets having a common master would, by definition, be synchronized and would use the same hopping sequence and would therefore actually constitute one and the same piconet.
A limited number of overlapping piconets can autonomously operate because of Bluetooth's frequency-hopping mechanism in which each piconet uses a different pseudo-random frequency hopping sequence wherein each pseudo-random sequence is seeded by the master's device address and is therefore a unique sequence. However, collisions are inevitable. Moreover, as the number of overlapping piconets are increased, collisions become increasingly likely and are problematic.
The IDC forecasts that by 2004 roughly 103.1 million Bluetooth® devices will be enabled in the U.S. and 451.9 million devices world wide. Consequently, the probability of interference resulting from neighboring piconets become increasingly probable. In the event of co-channel and adjacent interference, collisions occur which cause data packet retransmissions. The collisions and retransmissions result in a undesirable reduction in the data rate. Depending on the number, range, and comparable signal strength of neighboring piconets mitigating this interference is important. In many applications, such as voice over IP, even the smallest degradation in the signal is highly undesirable because it degrades the quality of the signal to an unusable degree. Moreover, in a typical office environment, the simultaneous operation of multiple Bluetooth® piconets will crowd the spectrum and increase the probability of signal degradation due to increased collision frequency.